JP6971901B2 - Sputtering target - Google Patents

Description

The present invention relates to a sputtering target, particularly a ferromagnetic material sputtering target used for forming a magnetic recording layer of a hard disk adopting a perpendicular magnetic recording method, and has low particle generation when sputtering with a magnetron sputtering apparatus. Regarding the target.
In the following description, the "sputtering target" is simply abbreviated as "target", but it means substantially the same thing. I will add it just in case.

In the field of magnetic recording represented by a hard disk drive, a material based on the ferromagnetic metals Co, Fe, or Ni is used as the material of the magnetic thin film responsible for recording. For example, a Co-Cr-based or Co-Cr-Pt-based ferromagnetic alloy containing Co as a main component has been used for the recording layer of a hard disk that employs an in-plane magnetic recording method.
Further, in the recording layer of the hard disk adopting the perpendicular magnetic recording method which has been put into practical use in recent years, a composite material composed of a Co—Cr—Pt-based ferromagnetic alloy containing Co as a main component and a non-magnetic inorganic substance is often used. ing.

In addition, ruthenium (Ru) alloy has excellent thermal stability, low resistance, and barrier properties, and is therefore attracting attention as a film forming material for semiconductor devices, especially as a gate electrode material and various diffusion barrier materials. There is.

Patent Document 1 (Patent No. 5394577) describes a sputtering target made of a metal having a composition in which Cr is 20 mol% or less, Ru is 0.5 mol% or more and 30 mol% or less, and the balance is Co, and the target is a metal. A Co-Ru alloy phase (B) containing 30 mol% or more of Ru in the substrate (A) and the (A), and a metal or alloy phase containing Co or Co as a main component different from the phase (B). A ferromagnetic material sputtering target characterized by having (C) is disclosed. Such a sputtering target becomes a target having a large leakage magnetic flux, and when used in a magnetron sputtering apparatus, it has an effect that the ionization of the inert gas is efficiently promoted and a stable discharge can be obtained.

However, Patent Document 1 has not sufficiently studied the generation of impurities and particles contained in the sputtering target containing Ru.

Patent Document 2 (Patent No. 5234735) is a ruthenium alloy sintered body target obtained by sintering a mixed powder of ruthenium powder and a metal powder that is easier to form an oxide than ruthenium, excluding gas components. The purity of the target is 99.95 wt% or more, the metal containing 5 at% to 60 at% of a metal that is easier to form an oxide than ruthenium is contained, the relative density is 99% or more, and the oxygen content as an impurity is 1000 ppm or less. A characteristic ruthenium alloy sputtering target is disclosed. Here, the reason why the oxygen content as an impurity is 1000 ppm or less is that a sputtering target having an oxygen content of more than 1000 ppm has a problem that the quality of film formation is deteriorated due to remarkable arcing and particle generation during sputtering. Because there is.

Japanese Patent No. 5394577 Japanese Patent No. 5234735

According to the invention according to Patent Document 2, a certain effect was obtained in suppressing the generation of particles during sputtering by setting the oxygen content as an impurity to 1000 ppm or less, but in recent years, throughout the life of the sputtering target. The demand for sputtering targets with a small number of particles generated is increasing, and the technology disclosed in Patent Document 2 may not be sufficient. The same applies to the invention according to Patent Document 1.

Therefore, it is an object of the present invention to provide a sputtering target containing a small number of particles generated throughout the life of the sputtering target by controlling impurities such as oxygen and carbon in the sputtering target containing Co and Ru.

As a result of further diligent examination of the relationship between impurities and the generation of particles in such a sputtering target containing Co and Ru, the present inventor has found that the particles generated during sputtering are carbon as impurities rather than oxygen as impurities. Was found to have a greater impact. It was also found that by reducing the content of carbon as an impurity to a certain amount or less, the generation of particles can be suppressed extremely effectively throughout the life of the sputtering target. The present invention has been completed based on such findings.

Therefore, the invention of the present application is specified as follows.
(1) Co is 50 to 90 at%, Ru is 10 to 50 at%, and the balance is a sputtering target composed of impurities. Among the impurities, oxygen exceeds 10,000 wtppm and carbon is 50 wtppm or less. A sputtering target characterized by.
(2) The sputtering target according to (1), wherein among the impurities, carbon is 30 wtppm or less.
(3) Further, one or more elements selected from the group consisting of Cr, Ti, Si, Ta, and B and oxygen existing in the form of an oxide are contained, and the Cr, Ti, Si, Ta, and B are contained. The sputtering target according to (1) or (2), wherein the amount of one or more elements selected from the group consisting of and oxygen present in the form of the oxide is 1 at% or more, respectively.
(4) The sputtering target according to any one of (1) to (3), wherein the relative density with respect to the theoretical density is 98.0% or more.

According to the present invention, it is possible to provide a sputtering target having excellent film forming property, which can effectively suppress the generation of particles during sputtering throughout the life of the sputtering target.

It is a figure which shows the relationship between the amount of carbon in a sputtering target, and the number of particles at the time of sputtering. It is a figure which further enlarged the vertical axis of FIG.

The main components constituting the sputtering target of the present invention are Co of 50 to 90 at%, Ru of 10 to 50 at%, and the balance consisting of impurities. Of the impurities, oxygen exceeds 10,000 wtppm and carbon is 50 wtppm or less. Is.

The above Co and Ru are added as essential components. When the amount of Co is 50 at% or more, ferromagnetism can be imparted to the entire sputtering target. On the other hand, if the amount of Co exceeds 90 at%, Ru becomes relatively small, and the effect of improving the performance by adding Ru is diminished, which is not desirable.
As for the above Ru, the effect of the magnetic thin film can be obtained from 10 at% or more, so the lower limit is set as described above. On the other hand, if the amount of Ru is too large, it is not preferable in terms of the characteristics as a magnetic material, so the upper limit is set to 50 at%.

Other than the above Co and Ru, the balance of the sputtering target becomes an impurity. Of the impurities, oxygen and carbon have the greatest effect on the performance of the sputtering target. Regarding oxygen, as described in Patent Document 2 described above, there is an effect of suppressing particles by setting it to 1000 ppm or less, but as described later, control of the carbon content in a sputtering target containing Co and Ru is far more. Since it is important, in the present invention, the amount of oxygen shall exceed 10,000 wtppm. When the amount of oxygen exceeds 10,000 wtppm, the effect of suppressing particles by setting the amount of carbon to 50 wtppm or less becomes more remarkable.

Of the impurities, it is important that the carbon content is 50 wtppm or less. The present inventor investigated the generation of particles during sputtering for a sputtering target containing Co and Ru, and found that the number of particles explosively increases when the carbon content exceeds 50 wtppm. Therefore, the carbon content is set to 50 wtppm or less. When the amount of carbon is 50 wtppm or less, not only the number of particles generated can be dramatically reduced, but also the increase in the number of particles generated can be suppressed extremely effectively throughout the life of the sputtering target. From this viewpoint, the carbon content is preferably 30 wtppm or less, more preferably 20 wtppm or less, and even more preferably 10 wtppm or less.

The carbon contained in the sputtering target includes not only the carbon contained in the raw material powder itself but also the carbon contained in the raw material powder diffused from the graphite die case when the raw material powder is sintered. In particular, since carbon is easily diffused into Ru, the amount of carbon in the sputtering target is often high.

The concentration of impurities can be measured by the inert gas melting method. For the carbon concentration, which is particularly important in the present invention, chips having a diameter of 100 mm and a thickness of 0.1 mm are collected from the center of the circle of each sputtering target with a lathe, and this sample is collected by a carbon analyzer [CECO, CSLS600]. Can be measured by the inert gas melting method.
The oxygen concentration can be measured by the inert gas melting method using the oxygen / nitrogen simultaneous analyzer [TC-600, manufactured by LECO] for the above sample.

In order to reduce the amount of carbon contained in the sputtering target, it is better to isolate the raw material powder in a graphite die case so that it does not come into direct contact with the graphite die case when hot-pressed. As a method of isolation, for example, alumina may be applied to the die case. It is also effective to lower the temperature condition in the hot press to reduce the carbon content.

Further, the sputtering target of the present invention can include one or more elements selected from the group consisting of Cr, Ti, Si, Ta, and B, and oxygen existing in the form of an oxide. When one or more elements selected from the group consisting of Cr, Ti, Si, Ta, and B and oxygen existing in the form of an oxide are contained, each is preferably 1 at% or more. In order to obtain such a composition, for example, at the time of manufacturing a sputtering target, a powder of Cr, Ti, Si, Ta, or B or an oxide powder of these Cr, Ti, Si, Ta, or B is used as a raw material powder. It may be added. By containing these elements, it has characteristics suitable for a material of a magnetic recording film having a granular structure, particularly a recording film of a hard disk drive adopting a perpendicular magnetic recording method. In particular, Cr demagnetizes the hcp structure of Co in the film without inhibiting it, and TiO ₂ has the effect of improving the separability between particles in the film.
The oxygen existing in the form of an oxide is not oxygen as an impurity.

The relative density of the sputtering target of the present invention is preferably 98.0% or more. In general, it is known that the higher the density of the target, the smaller the amount of particles generated during sputtering. Similarly in the present invention, it is preferable to have a high density. From the above viewpoint, the relative density of the target is more preferably 99.0% or more, and even more preferably 99.5% or more.

In the present invention, the relative density is a value obtained by dividing the measured density of the target by the calculated density (also referred to as the theoretical density). The calculated density is the density when it is assumed that the constituent components of the target are mixed without being diffused or reacted with each other, and is calculated by the following equation.
Formula: Calculated density = Σ (molecular weight of constituents x molar ratio of constituents) / Σ (molecular weight of constituents x molar ratio of constituents / literature value density of constituents)
Here, Σ means that the sum is taken for all the constituent components of the target.

Further, the sputtering target of the present invention can be selected from carbon, oxides, nitrides, carbides and carbonitrides and may contain one or more inorganic materials. In this case, it has characteristics suitable for a material of a magnetic recording film having a granular structure, particularly a recording film of a hard disk drive adopting a perpendicular magnetic recording method.

(Production method)
The manufacturing method of the tungsten sputtering target of the present invention is not particularly limited as long as it has each of the above-mentioned characteristics, but powder sintering is used as a means for obtaining a sputtering target having such characteristics. Using the method, for example, it can be produced by the following method. First, a particle powder in which Co and Ru are dispersed in each other is prepared, and these are weighed so as to have a desired target composition to obtain a powder for sintering. This can be sintered by hot pressing or the like to produce the sputtering target of the present invention.

Co metal powder and Ru metal powder are used as starting materials. It is desirable to use Co metal powder and Ru metal powder having a maximum particle size of 150 μm or less, more preferably 50 μm or less, and further preferably 20 μm or less. Further, when a metal oxide powder is used, it is desirable to use a powder having a maximum particle size of 100 μm or less, more preferably 20 μm or less, still more preferably 5 μm or less. If the particle size is too small, it tends to aggregate, so it is more desirable to use one with a particle size of 0.1 μm or more.

The raw material powder is weighed so as to have a desired target composition, and is mixed together with pulverization by using a known method such as a ball mill. The sintering powder thus obtained is molded and sintered by hot pressing. In addition to the hot press, a plasma discharge sintering method and a hot hydrostatic pressure sintering method can also be used. It is preferable to set the holding temperature at the time of sintering to the lowest temperature in the temperature range where the target is sufficiently densified. Depending on the composition of the target, it is often in the temperature range of 900-1300 ° C. Through the above steps, a sintered body for a ferromagnetic material sputtering target can be manufactured.

In hot pressing, it is important to separate the raw material powder from the die case in order to keep the carbon content in the obtained sputtering target to 50 wtppm or less. As a method of isolation, for example, alumina may be applied to the die case.

The sputtering target according to the present invention can be produced by molding the obtained sintered body into a desired shape using a lathe or the like. The target shape is not particularly limited, and examples thereof include a flat plate shape (including a disk shape and a rectangular plate shape) and a cylindrical shape. The sputtering target according to the present invention is particularly useful as a sputtering target used for forming a granular structure magnetic thin film.

Examples of the present invention are shown below together with comparative examples, but these examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the present invention. ..

(Example 1, Example 2, Example 3 and Comparative Example 1)
As raw material powders, Co powder having an average particle size of 3 μm, Cr powder having an average particle size of 3 μm, Ru powder having an average particle size of 3 μm, and TiO ₂ powder having an average particle size of 1 μm were prepared.
Co powder 58.24 wt%, Cr powder 3.43 wt%, Ru powder 26.64 wt%, TiO ₂ powder 7 so that the target composition of these powders is 50Co-20Cr-20Ru-10TIO _{2 (mol%).} Weighed at a weight ratio of 0.01 wt%.

Next, Co powder, Cr powder, Ru powder, and TiO ₂ powder were sealed in a ball mill pot having a capacity of 10 liters together with zirconia balls as a pulverizing medium, and rotated for 20 hours to mix.

This mixed powder is filled in a carbon mold, and the temperature is 1100 ° C., 1000 ° C., 900 ° C. for each example, the holding time is 2 hours, and the temperature is 1100 ° C. for Comparative Example 1 in a vacuum atmosphere under the condition of a pressing force of 30 MPa. , Hot-pressed with a holding time of 2 hours to obtain a sintered body. At the time of sintering, alumina was applied to the die case for Example 1, but in Example 2, Example 3 and Comparative Example 1, alumina was not applied to the die case, and the raw material powder and the die case were not separated.
Further, these sintered bodies were ground by using a surface grinding machine to obtain a disk-shaped target having a diameter of 180 mm and a thickness of 5 mm.

(Impurity concentration)
For the carbon concentration, chips of 100 mm in diameter × 0.1 mm in thickness were collected from the center of the circle of each sputtering target with a lathe, and this sample was collected using a carbon analyzer [CECO, CSLS600] as an inert gas. It was measured by the melting method.
The oxygen concentration was measured by the inert gas melting method using the oxygen / nitrogen simultaneous analyzer [TC-600, manufactured by LECO].

(Number of particles)
Next, this target was attached to a DC magnetron sputtering device and sputtering was performed. The sputtering conditions were a sputtering power of 1.0 kW, an Ar gas pressure of 1.7 Pa, and a sputtering time of 20 seconds, and sputtering was performed on a silicon substrate having a diameter of 4 inches. Then, the number of particles adhering to the substrate was measured with a particle counter. This sputtering was carried out so that the target life was 3kWhr or more, and the number of particles generated at each time point was measured.

The results of Example 1, Example 2, Example 3, and Comparative Example 1 are shown in Table 1, FIG. 1, and FIG.

(Example 4 and comparative example 2)
As raw material powders, Co powder having an average particle size of 3 μm, B powder having an average particle size of 3 μm, Ru powder having an average particle size of 3 μm, and SiO ₂ powder having an average particle size of 1 μm were prepared.
Co powder 78.77 wt%, B powder 1.85 wt%, Ru powder 17.32 wt%, SiO ₂ powder 2 so that the target composition of these powders is 78Co-10B-10Ru-2SiO _{2 (mol%).} Weighed at a weight ratio of .06 wt%.

Next, Co powder, B powder, Ru powder, and SiO ₂ powder were sealed in a ball mill pot having a capacity of 10 liters together with zirconia balls as a pulverizing medium, and rotated for 20 hours to mix.

This mixed powder was filled in a carbon mold and hot-pressed in a vacuum atmosphere under the condition of a pressing force of 30 MPa at a temperature of 1100 ° C. and a holding time of 2 hours to obtain a sintered body. At the time of sintering, alumina was applied to the die case in Example 4, but in Comparative Example 2, alumina was not applied to the die case, and the raw material powder and the die case were not separated.
Further, these sintered bodies were ground by using a surface grinding machine to obtain a disk-shaped target having a diameter of 180 mm and a thickness of 5 mm.

(Impurity concentration)
For the carbon concentration, chips of 100 mm in diameter × 0.1 mm in thickness were collected from the center of the circle of each sputtering target with a lathe, and this sample was collected using a carbon analyzer [CECO, CSLS600] as an inert gas. It was measured by the melting method.
The oxygen concentration was measured by the inert gas melting method using the oxygen / nitrogen simultaneous analyzer [TC-600, manufactured by LECO].

(Number of particles)
Next, this target was attached to a DC magnetron sputtering device and sputtering was performed. The sputtering conditions were a sputtering power of 1.0 kW, an Ar gas pressure of 1.7 Pa, and a sputtering time of 20 seconds, and sputtering was performed on a silicon substrate having a diameter of 4 inches. Then, the number of particles adhering to the substrate was measured with a particle counter. This sputtering was carried out so that the target life was 3kWhr or more, and the number of particles generated at each time point was measured.

The results of Example 4 and Comparative Example 2 are shown in Table 1.

(Example 5 and Comparative Example 3)
As raw material powders, Co powder having an average particle size of 3 μm, Ru powder having an average particle size of 3 μm, and CoO powder having an average particle size of 1 μm were prepared.
These powders were weighed in a weight ratio of 72.82 wt% of Co powder, 15.61 wt% of Ru powder, and 11.57 wt% of CoO powder so that the target composition was 80Co-10Ru-10CoO (mol%).

Next, Co powder, Ru powder and CoO powder were sealed in a ball mill pot having a capacity of 10 liters together with zirconia balls as a pulverizing medium, and rotated for 20 hours to mix.

This mixed powder was filled in a carbon mold and hot-pressed in a vacuum atmosphere under the condition of a pressing force of 30 MPa at a temperature of 1100 ° C. and a holding time of 2 hours to obtain a sintered body. At the time of sintering, alumina was applied to the die case in Example 5, but in Comparative Example 3, alumina was not applied to the die case, and the raw material powder and the die case were not separated.
Further, these sintered bodies were ground by using a surface grinding machine to obtain a disk-shaped target having a diameter of 180 mm and a thickness of 5 mm.

(Impurity concentration)
For the carbon concentration, chips of 100 mm in diameter × 0.1 mm in thickness were collected from the center of the circle of each sputtering target with a lathe, and this sample was collected using a carbon analyzer [CECO, CSLS600] as an inert gas. It was measured by the melting method.
The oxygen concentration was measured by the inert gas melting method using the oxygen / nitrogen simultaneous analyzer [TC-600, manufactured by LECO].

(Number of particles)
Next, this target was attached to a DC magnetron sputtering device and sputtering was performed. The sputtering conditions were a sputtering power of 1.0 kW, an Ar gas pressure of 1.7 Pa, and a sputtering time of 20 seconds, and sputtering was performed on a silicon substrate having a diameter of 4 inches. Then, the number of particles adhering to the substrate was measured with a particle counter. This sputtering was carried out so that the target life was 3kWhr or more, and the number of particles generated at each time point was measured.

The results of Example 5 and Comparative Example 3 are shown in Table 1.

(Example 6 and Comparative Example 4)
As raw material powders, Co powder having an average particle size of 3 μm, Ru powder having an average particle size of _{3 μm, and Cr 2} O 3 powder having an average particle size of 1 μm were prepared.
Weight of Co powder 35.70 wt%, Ru powder 55.10 wt%, Cr ₂ O ₃ powder 9.20 wt% so that the target composition of these powders is 50 Co-45 Ru-5 Cr ₂ O _{3 (mol%).} Weighed by ratio.

Next, Co powder, Ru powder and Cr ₂ O ₃ powder were sealed in a ball mill pot having a capacity of 10 liters together with zirconia balls as a pulverizing medium, and rotated for 20 hours to mix.

This mixed powder was filled in a carbon mold and hot-pressed in a vacuum atmosphere under the condition of a pressing force of 30 MPa at a temperature of 1100 ° C. and a holding time of 2 hours to obtain a sintered body. At the time of sintering, alumina was applied to the die case in Example 6, but in Comparative Example 4, alumina was not applied to the die case, and the raw material powder and the die case were not separated.
Further, these sintered bodies were ground by using a surface grinding machine to obtain a disk-shaped target having a diameter of 180 mm and a thickness of 5 mm.

(Impurity concentration)
For the carbon concentration, chips of 100 mm in diameter × 0.1 mm in thickness were collected from the center of the circle of each sputtering target with a lathe, and this sample was collected using a carbon analyzer [CECO, CSLS600] as an inert gas. It was measured by the melting method.
The oxygen concentration was measured by the inert gas melting method using the oxygen / nitrogen simultaneous analyzer [TC-600, manufactured by LECO].

(Number of particles)
Next, this target was attached to a DC magnetron sputtering device and sputtering was performed. The sputtering conditions were a sputtering power of 1.0 kW, an Ar gas pressure of 1.7 Pa, and a sputtering time of 20 seconds, and sputtering was performed on a silicon substrate having a diameter of 4 inches. Then, the number of particles adhering to the substrate was measured with a particle counter. This sputtering was carried out so that the target life was 3kWhr or more, and the number of particles generated at each time point was measured.

The results of Example 6 and Comparative Example 4 are shown in Table 1.

From the results of Table 1, FIG. 1 and FIG. 2, it was found that the number of particles generated during sputtering was dramatically reduced by setting the carbon content in the sputtering target to 50 wtppm or less. It was also found that by further reducing the carbon content to 30 wtppm or less, the number of particles hardly increased throughout the life of the sputtering target.
On the other hand, in Comparative Example 1, since the carbon content was 380 wtppm, the number of particles increased explosively after the start of sputtering.
In Comparative Example 2, since the carbon content was 80 wtppm, the number of particles increased explosively after the start of sputtering.
In Comparative Example 3, since the carbon content was 100 wtppm, the number of particles increased explosively after the start of sputtering.
In Comparative Example 4, since the carbon content was 140 wtppm, the number of particles increased explosively after the start of sputtering.

Claims (4)

It is a sputtering target in which Co is 50 to 90 at%, Ru is 10 to 50 at%, and the balance is impurities, and among the impurities, oxygen exceeds 10,000 wtppm and carbon is 50 wtppm or less. Sputtering target. The sputtering target according to claim 1, wherein among the impurities, carbon is 30 wtppm or less. Further, one or more elements selected from the group consisting of Cr, Ti, Si, Ta, and B, and oxygen existing in the form of an oxide are contained, and the group consisting of Cr, Ti, Si, Ta, and B. The sputtering target according to claim 1 or 2, wherein the amount of one or more elements selected from the above and oxygen present in the form of the oxide is 1 at% or more, respectively. The sputtering target according to any one of claims 1 to 3, wherein the relative density with respect to the theoretical density is 98.0% or more.

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